bgo#327152 - Ellipsize long directory names in GtkPathBar, and better layout for...

bgo#327152 - Ellipsize long directory names in GtkPathBar, and better layout for the pathbar

Ellipsize labels in the Save folder's combo so they don't grow too wide.

Ellipsize labels in normal directory buttons in the pathbar, and make
their requisition's width reasonably small.  Use a tooltip for buttons
that got ellipsized.

Instead of placing the down-slider directly beside the last button in
the pathbar, use the remaining space in the pathbar for the last
button.  Use a different method to find the first visible button.
Walk down from the end, adding buttons until we use all free space.

Signed-off-by: Federico Mena Quintero <federico@novell.com>